Above: A device monitors noise levels in a residential neighborhood adjacent to a Quiet Pavement Pilot Program freeway segment. Photo: Arizona DOT. Below: This trailer—built by the National Center for Asphalt Technology—is used to directly measure tire/pavement noise levels using the close-proximity method. Photo: NCAT

Asphalt pavements constructed with an open-graded friction course have been proven to generate less traffic-related noise than traditional hot-mix asphalt pavements. Photo: NCAT

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Europe—the quiet continent

Quiet pavement is nothing new to Europeans. The technology has been widely used in Europe for many years. In spring 2004, an International Scanning Tour—sponsored by the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the Transportation Research Board—visited Denmark, the Netherlands, France, Italy, and the United Kingdom to learn more about general noise reduction practices in Europe.

Tour participants found that three major pavement technologies are used in Europe to mitigate noise. These include the use of thin surfaced, negatively textured gap-graded asphalt mixes primarily used in urban locations and areas subject to severe winter weather; single- and double-layer, highly porous asphalt mixes used in rural locations with moderate winter conditions; and exposed-aggregate pavements used in areas of concrete pavement construction.

European countries are continuing in their commitment to lower traffic noise levels along roadways. The United Kingdom established a goal to resurface 60% of major roads with quieter materials over a 10-year period. The countries of the European Union have agreed to map noise contours along all existing roadways by 2007. Then each country will develop an action plan to address noise-related problems identified by this map.

More information about the team's findings can be found at http://146.6-177.170.

What's the concrete industry doing about noise?

The concrete pavement industry is working to address one form of noise—sound at the tire/pavement interface—commonly called tire/pavement noise. The American Concrete Pavement Association (ACPA) is pursuing research and testing with two things in mind, said Gerald F. Voigt, ACPA president and CEO. "We will not trade off safety or long-term performance, and we will strive to avoid significantly increasing initial costs or life-cycle costs," he said.

The answer to achieving a relatively quiet concrete pavement often lies in the pavement's texture. Since the late 1970s, the Federal Highway Administration (FHWA) has required concrete pavement surfaces being used on federally funded highway applications to be textured. This led to the widespread use of transverse tining on concrete pavements, now known to produce loud, whining road noise in many areas.

The concrete pavement industry presently has powerful tools to produce quiet, safe, and smooth pavements, according to Steve Waalkes, P.E., ACPA's managing director of technical service. "We're opening up the industry to new ideas," said Waalkes. "There are alternative textures that are just as safe as transverse tining."

He cited longitudinal tining, Astroturf drag, and other methods for imparting texture. Diamond grinding also can improve both smoothness and sound qualities, Waalkes said. "Diamond grinding is used successfully to restore the smoothness and texture of existing pavements, and in some cases to enhance the qualities of new pavements."

A number of tire-pavement noise research and testing initiatives are currently underway, according to Larry Scofield, P.E., ACPA's director of environmental engineering, including:

Field experiments—The Center for Portland Cement Concrete Pavement Technology/FHWA/ACPA are working together on a far-reaching research project to evaluate pavement surface characteristics. The research seeks to understand the relationship between noise and pavement texturing (and grinding for imparting texture); to evaluate the noise/texture/time relationship; and to develop construction techniques that are repeatable and cost-effective.

Laboratory testing—At Purdue University—and with support from the ACPA and its affiliate, the International Grooving and Grinding Association (IGGA)— testing is being conducted using a custom-built grinding head, a key component of the tire-pavement test apparatus.

Sound intensity testing—ACPA has invested in an apparatus to conduct tire/pavement noise testing. Scofield noted that ACPA and the IGGA are conducting limited evaluations for contractors and agencies using a well-defined and consistent protocol that employs a standard test vehicle and specific brand and type of tires.

Other field testing—ACPA has conducted or participated in field experiments in Arizona, Kansas, and California. Scofield noted that these field evaluations are yielding some surprising and positive results that underscore the benefits of certain existing technologies used to impart surface characteristics.

For questions or additional information about tire/pavement noise and pavement surface characteristic research initiatives, contact Larry Scofield at 480-775-0908.